Highlight-color printers typically print text in one, primary color, usually black, and can print areas of highlight color (e.g., borders, signatures, underlines, etc.), in another primary color such as blue, green, or red. In well-known highlight-color printers, the photo-conductor is charged in the form of an image where some areas are charged positively and some areas are charged negatively relative to non-image areas. Then, using a black toner with a positive potential and a color toner with a negative potential, both black text and colored highlight areas are developed and printed on a substrate in a single pass. Such a system is described, for example, in U.S. Pat. No. 5,208,636 to Rees et al., issued May 4, 1993, the teachings of which are hereby incorporated by reference in their entirety. Highlight colorant can be any color for which a toner has been developed. One or both toners may be applied to paper or similar substrates in various combinations, such as by halftoning, so as to expand the range of apparent colors available from the printer. For example, the resultant variations with red highlight and black toner can vary from white, light pink and light gray to red or black.
Various document composition and set-up systems exist to support highlight color output devices but the output of these conventional systems are incompatible with full-color devices and their required image descriptions. Accordingly, the present invention is directed to a method to convert two-color definitions designed for highlight color printing systems to full-color definitions in order to take advantage of advanced color-rendering algorithms and to facilitate the migration of highlight-color applications to full-color-printers.
Heretofore, several patents disclosed the concepts of two-or highlight-color ink catalogs and associated data streams to operate highlight-color printers. The following patents are hereby incorporated by reference in their entirety:
U.S. Pat. No. 5,134,493 to Laman et al., issued Jul. 28, 1992, discloses a language for describing image colors in an organized manner, wherein the language names primary colors, color catalogs and palettes within catalogs, bitmaps used to create the palette colors which include screens, and the actual palette colors themselves (defined by combinations of defined colors, bitmaps and screens), which may be loaded into highlight-color printers for rendering.
U.S. Pat. No. 5,153,739 to Laman et al., issued Oct. 6, 1992, teaches a printing system in which a variety or colors and shapes are created and may be stored as though they were fonts, and then rendered so as to produce highlight and/or multi-color images.
U.S. Pat. No. 5,237,425 to Tagami et al., issued Aug. 17, 1993, discloses a compiler for producing, from an Ink Source Language, a catalog of colors using two colorants (e.g., black plus highlight color) for use in a printer.
The present invention is directed to a method to take a named, two-color definition and convert that two-color definition from the form used in highlight-color page composition and print systems into a full-color representation in order to enable the use of the two-color definitions on full-color printers. The method allows full-color marking engines to be used in what may have been a highlight-color only environment. The method employs at least one function, which may be user-defined, to produce a standard full-color representation (e.g., sRGB) for various combinations of two toner colors (e.g., highlight plus black). The sRGB definition can then be used in a printer-independent manner on monochrome, highlight, or full-color printers using existing color-rendering algorithms. In one embodiment a user can vary or fine-tune the conversion by altering the behavior of the user-supplied functions.
In accordance with the present invention, there is provided a method for converting input data representing a color formed from only two primary colors to output data representing a color in a full-color space, comprising the steps of: receiving the two-color input data in the form of two colors, a primary color and a secondary color; mapping each color of the two-color input data to an equivalent color defined in the full color space by applying a first mapping function to each color of the two-color input data; determining, from the two-color input data, a rendering (screen) characteristic for each of the primary color and the secondary color; based upon the rendering characteristics, and the primary and secondary colors, representing a combination of the primary and secondary colors, and the associated rendering characteristics, as an intermediate output; and processing the intermediate output using a second function to generate the output data representing a single color defined in the full color space.
In accordance with another aspect of the present invention, there is provided a method for converting input data representing a color formed from only two primary colors to output data representing a color formed from at least three colors, comprising the steps of: receiving the two-color input data in the form of two colors, a primary color and a secondary color; determining, for each color of the two-color input data, an equivalent color defined in a full-color space by applying a first function to each color of the two-color input data; determining, from the two-color input data, a screen characteristic for the primary color and the secondary color; determining which screen characteristic is of a lesser value, and then determining if the lesser value is equal to zero; if the screen characteristic is zero, generating an intermediate output that is a function of only one of the primary and secondary colors, otherwise, generating an intermediate output that is a function of both the primary and secondary colors, wherein the intermediate outputs include a highlight color, a highlight color percentage and a black percentage; and processing the intermediate output using a second function to generate the output data representing a single color defined in at least three color space.
In accordance with yet another aspect of the present invention, there is provided a method of instructing a printing system which prints in at least three colorants to print a predetermined color defined using only a first and second color, comprising the steps of: creating a schema to represent said first and second colors, said palette including, palette names and colorant names, for generating different colors; using a processor, determining, for each color of the two-color input data, an equivalent color defined in a full-color space by applying a first function to each color of the two-color input data; determining, from the two-color input data, a screen characteristic for the primary color and the secondary color; determining which screen characteristic is of a lesser value, and then determining if the lesser value is equal to zero; if the screen characteristic is zero, generating an intermediate output that is a function of only one of the primary and secondary colors, otherwise, generating an intermediate output that is a function of both the primary and secondary colors, wherein the intermediate outputs include a highlight color, a highlight color percentage and a black percentage; and processing the intermediate output using a second function to generate the output data representing a single color defined in at least three color space and storing said output data in a schema.
The present invention finds particular advantage because of its ability to convert existing color-rendering mechanisms to a form suitable for new, full-color target printers. The present method can be applied in real time as each highlight-color combination is identified, converted as required, and passed immediately to the rendering algorithm. Alternatively, it can be pre-applied to an entire set of color combinations in ink catalogs (e.g., upon installation of each ink catalog on the target printer) and the results stored in a pre-defined format, which are subsequently used in the manner of a look-up table for rendering.
The present invention will be described in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.